It has been generally known for years that treating fibrous vegetable substances with pressurized steam will contribute to the breakdown of the fibers. In addition, steam treatment has been used in conjunction with chemical additives, usually some form of ammonia and alkaline materials, to also modify tobacco properties. For example, one long expired patent, U.S. Pat. No. 42,319 to Jacob S. Storer (1864), teaches treating the fibrous part of plants (such as, straw, grasses, leaves, or stems of plants having long staple or woody fibers) with chemicals (such as, potash, soda, soda ash, ammonia, lime or salts) and by mediation of steam, dissolve out undesirable compounds that would impair the material's quality or color. U.S. Pat. No. 2,032,437 to Richter (1936) teaches a process whereby fiber is liberated from wood or other raw cellulosic material by the chemical action of a digester liquid, such as a sulfite or acid sulfite cooking liquor, while under confinement. U.S. Pat. No. 2,964,518 to Snyder (1960) teaches a process in which woody materials are subjected to the action of ammonia and steam at pressures in the range of 600 to 1250 PSIG and temperatures of about 250.degree. to 300.degree. C. for up to 90 minutes to separate the fibrous and ligneous portions of the material.
It is also generally known in the tobacco processing art to use steam and chemicals as a means for forming flavor compounds in tobacco. U.S. Pat. No. 4,607,646 to Lilly, Jr., et al. (1986) teaches reacting ammonia with non-burley tobacco containing natural sugars, in a pressure controlled system heated to temperatures of 80.degree. to 150.degree. C. in order to impart burley-like smoke flavor characteristics, yet retain substantially all volatile tobacco components. Several other patents are known that relate to processes for treating tobacco to form flavor compounds. U.S. Pat. No. 4,677,994 to Denier et al. (1987) teaches treating, drying and expanding tobacco by applying an ammonia source to the tobacco, then treating the ammoniated tobacco with steam for a preselected time, with the result being improved flavor quality and fill value of the tobacco. U.S. Pat. No. 4,744,375 to Denier et al. (1988) teaches introducing moistened tobacco into a containing zone, introducing an ammonia source, and heating the contained zone to bring the tobacco to a preselected temperature to produce flavor compounds in the tobacco. U.S. Pat. No. 4,825,884 to Denier et al. (1989) teaches contacting the tobacco with citrus pectin, invert sugar, or diammonium phosphate, or a combination thereof, introducing the moistened tobacco into a containing zone along with an ammonium source, and heating the containing zone to bring the tobacco to a preselected temperature to produce flavor compounds in the tobacco.
In the main, the past tobacco treating art has utilized various combinations of steam, ammonia or chemicals in treating tobacco materials in order to form flavor compounds or to break down the lignin and cellulose in wood products to form by-products useful in manufacturing other goods.